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Decay-Assisted Laser Spectroscopy of Neutron-Deficient Francium

K. M. Lynch, J. Billowes, M. L. Bissell, I. Budinčević, T. E. Cocolios, R. P. De Groote, S. De Schepper, V. N. Fedosseev, K. T. Flanagan, S. Franchoo, R. F. Garcia Ruiz, H. Heylen, B. A. Marsh, G. Neyens, T. J. Procter, R. E. Rossel, S. Rothe, I. Strashnov, H. H. Stroke, and K. D. A. Wendt
Phys. Rev. X 4, 011055 – Published 28 March 2014
Physics logo See Synopsis: Picking Nuclei with Lasers

Abstract

This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes Fr202206 performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay-spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes Fr202206, in addition to the identification of the low-lying states of Fr202,204 performed at the CRIS experiment.

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  • Received 6 January 2014

DOI:https://doi.org/10.1103/PhysRevX.4.011055

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Synopsis

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Picking Nuclei with Lasers

Published 28 March 2014

A laser-based scheme allows the preparation of pure samples of nuclear isomers for spectroscopic analysis.

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Authors & Affiliations

K. M. Lynch1,2,3,*, J. Billowes1, M. L. Bissell3, I. Budinčević3, T. E. Cocolios1,2, R. P. De Groote3, S. De Schepper3, V. N. Fedosseev4, K. T. Flanagan1, S. Franchoo5, R. F. Garcia Ruiz3, H. Heylen3, B. A. Marsh4, G. Neyens3, T. J. Procter1,†, R. E. Rossel4,6, S. Rothe4,6, I. Strashnov1, H. H. Stroke7, and K. D. A. Wendt6

  • 1School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom
  • 2ISOLDE, PH Department, CERN, CH-1211 Geneva-23, Switzerland
  • 3Instituut voor Kern- en Stralingsfysica, KU Leuven, B-3001 Leuven, Belgium
  • 4EN Department, CERN, CH-1211 Geneva 23, Switzerland
  • 5Institut de Physique Nucléaire d’Orsay, F-91406 Orsay, France
  • 6Institut für Physik, Johannes Gutenberg-Universität Mainz, D-55128 Mainz, Germany
  • 7Department of Physics, New York University, New York, New York 10003, USA

  • *kara.marie.lynch@cern.ch
  • Present address: TRIUMF, Vancouver, British Columbia V6T 2A3, Canada.

Popular Summary

The atomic nucleus, a mix of protons and neutrons, was discovered more than a century ago, but many key questions about its structure and the underlying nuclear force remain unanswered: What determines the shape of a nucleus? What are its quantum-mechanical states? A nucleus can have a number of isotopic neighbors, differing only in the number of neutrons. How are such neighbors related? Laser spectroscopy, in which atomic nuclei can be selectively excited and analyzed by lasers, has greatly expanded our ability to address these questions. In this experimental paper, we present a novel method of laser spectroscopy and its applications to the study of rare neutron-deficient francium isotopes, with a number of new results.

Francium isotopes, while highly radioactive and extremely rare in natural existence, have been successfully synthesized in the laboratory and offer the unique opportunity to answer questions about the nuclear structure in their region of the nuclear chart under the interrogations of laser spectroscopy. In our experiment, radioactive beams of francium isotopes are produced at the ISOLDE facility at CERN, to which our new technique, called decay-assisted Collinear Resonance Ionization Spectroscopy, is applied. Two laser beams overlap collinearly with the isotope beams: The first tunable laser excites the atoms, probing their hyperfine structure, and the second laser ionizes them. The ion beam is deflected to a decay spectroscopy station, where events of radiative alpha decays are tagged, providing identification of the hyperfine components. From the hyperfine structure, fundamental observables of the nucleus can be extracted without reliance on theoretical nuclear models. Indeed, we have succeeded in making the first measurement of the magnetic dipole moments and the change in the average charge radii of isotopes Fr202206, for both their ground and low-energy isomeric (metastable) states.

The high resolution intrinsic to the collinear resonance ionization process combined with the high efficiency of ion detection makes our technique a highly sensitive one to probe the hyperfine structure and extract fundamental nuclear observables of exotic nuclear isotopes (and isomers) beyond the francium family.

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Vol. 4, Iss. 1 — January - March 2014

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